The present invention relates to packaging laminates for bags, more particularly for industrial covers.
In industrial packaging, various packaging laminates are conventionally formed by gluing an aluminum foil on one side to a polyester layer and on the other side to a plastic film such as polyethylene, in order to protect items packaged in the cover from moisture and contaminants. This implies that the layers of the laminate should be flat because the quantity of glue should be small, otherwise the laminate becomes stiff and difficult to handle. The cover is generally treated with a vacuum pump which puts the items inside the cover under a partial vacuum. A quantity of drying agent, such as silica gel, the amount of which is calculated according to the volume of the bag and the country of destination (due to weather conditions to be expected there), is inserted into the cover to absorb moisture.
This system suffers from various problems both from a technical point of view and in the method being used to protect items.
First, the prior art cover laminates are not strong enough. They have a poor tear resistance, initiated tear resistance and puncture resistance. During the manufacture of the covers, they are frequently torn out by sharp edged items and have to be replaced.
Most items to be packaged have irregular shapes and this problem may occur a number of times. Even after arrival at the destination, a simple sharp edge may compromise the cover, making the content of the cover unusable. Consequently, the packager has to reinforce acute angles of the item inside the cover by a protecting material. But even with such a reinforcement material, problems usually occur. Moreover the reinforcement material is generally an open cell material which has absorbed moisture. The material exhausts the moisture inside the cover, which may lead to corrosion of the items packaged. Thus, users of such packages are faced with high production costs due to the replacement of covers, the reinforcement material being used, the labor costs involved and further problems when items arrive at a destination and are stored for a period of time. Moreover, it is not 100% sure that the items packaged will be well protected during the transportation.
Secondly, the prior art cover materials have a board-like metallic aspect and are quite hard to handle and conveniently fold. Consequently, during their manipulation, various weakening points appear mainly at the folded parts of the cover and the aluminum foil is partially destroyed, making a pinhole cloud noticeable by transparency. These defects are not 100% visible to the workers because they are not supposed to check the products, but to weld them.
Thirdly, the prior art cover materials are made by lamination with glue applied at a low temperature. Since welding of the seals is carried out at a high temperature (190 to 220xc2x0 C.), the chemical structure of the glue is altered and the welded seals are partly destroyed. They are so weak that even the producers draw customers"" attention on them in their specification sheets. The only advantage of the glue is that it reinforces the tensile strength of the final product, but artificially, because the main characteristics are given by the other components which are generally not as strong.
Fourthly, the prior art cover materials have a small heat conductivity because heat applied by a welding grip is not easily transferred. Only the aluminum foil has a high heat conductivity and heat has to be applied longer with a high pressure, which also leads to a destruction of the glue and to poor seals.
Fifthly, prior art cover materials have no good water vapor transmission rate. Since the polyester is a transparent sheet of only 12 xcexcm thickness and the back side is a polyethylene sheet of 80/90 xcexcm thicknessxe2x80x94both products being quite vapor permeablexe2x80x94the main permeation rate is given by the aluminum foil (9 xcexcm or 7 xcexcm thickness). It is to be noticed that the water vapor transmission rate of transparent polyester is as high as +/xe2x88x92 20 g/sqm/24 hours and is more or less the same for polyethylene. This is to be compared with the water vapor transmission rate required by the American standard MIL B 131 H which is only 0.3 g/sqm/24 hours. The aluminum foil is quite thin and can be partially destroyed during the manufacture of the cover. Moreover the glue is quite hard and when the product is folded glue particles may be pushed into the foil and damage it severely. Consequently, the prior art cover materials are not 100% reliable for their water vapor transmission rate which is quite high even if it is within the requirements of the American standard specifications.
Sixthly, due to the various above-mentioned problems, the process used to protect goods by quick exhaustion of the inner atmosphere by a vacuum pump is poor, because the covers are not 100% gas-proof and after a certain time moisture-loaded air substantially enters the covers and the drying agent is soon saturated. Others have tried to inject nitrogen into the covers to dry the items inside, but the problems remain and various customers have experienced substantial damage even if everything seemed to be correct when their goods were packed.
In summary, prior art cover materials are quite poor in their characteristics and even dangerous for the valuable goods they are supposed to protect. Moreover, even if their price is quite low, they incur substantial additional costs due to all the problems arising during their manufacture and later on upon their transportation and storage. Added insurance costs are also a consequence.
Consequently, there remains a need on the market for improved high barrier cover materials with a very low water vapor transmission rate, with high tear, puncture, initiated tear and impact resistance, easily sealable and quite flexible. The improved cover material may be used in a temperature range between 40 and 70xc2x0 C. The improved cover material should have also an excellent quality/price ratio.
The present invention relates to new improved cover laminates with high level performances for forming covers for industrial packaging, which comprises substantially one layer of metallized polyester, and one or two layers of a special polyethylene to be discussed more in detail below.
In one aspect, the laminate is made by an extrusion process carried out at 300xc2x0 C. and the interlayers are formed with a special polyethylene mix discussed further in the specification.
In another aspect, the laminate is made partly by extrusion and partly by glue lamination to improve price while maintaining high performance characteristics.
The laminates are useful for making covers for protecting industrial and/or military items of high value during their transportation and/or storage, with or without an inerting gas system. The various items include all types of machinery, spare parts, complete plants, tanks, weapons, missiles, bombs, explosives, planes, but also items as small as electronic chips.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify these embodiments.